A conventional ball valve shown in FIGS. 1 and 2 includes a housing 1, a valve member 2, and a grip 22. The housing 1 is provided with a valve chamber 10 in the center 12 portions and an inlet portion 11 and an outlet portion respectively at two sides of the valve chamber 10 and a shaft hole 13 formed in an upper center portion.
The valve member 2 consists of a valve portion and a shaft portion 21 extending up from the valve portion, and the valve portion has a cavity 20 to align or not to align to the inlet portion 11 and the outlet portion 12 so that the valve portion together with the shaft portion 21 may be rotated by the grip 22 fitted with the upper end of the shaft portion 21 for opening and closing the ball valve. The shaft portion 21 has an anti-leak gasket fixed around the lower end of the shaft portion to prevent liquid in the ball valve from leaking through the gap between the shaft portion and the shaft hole of the housing 1. In fabricating the ball valve, the valve member is formed in advance, and then placed in a mold for injecting molding the housing 1 to combine the valve member 2 in the housing 1.
However, In the molding process of the housing 1, the mold is heated up to a high temperature of about 200° C. to produce some damage to the outer surface of the valve member 2, so the contact areas of the shaft portion 21 with a coarse rough surface 210 and the shaft hole 13 may not be very close enough as they should be for anti-leakage. Moreover, the coarse surface 210 of the shaft portion 21 may cause extremely large friction to hamper smooth rotation of the valve member 2 in opening and closing the ball valve, affecting the service life of the ball valve.
A valve assembly disclosed in two U.S. Pat. No. 5,865,210 and U.S. Pat. No. 4,088,299 includes a body 10 and a valve closure member 14 separately formed and combined together. So they have a flaw of complicated manufacturing processes, expensive cost, with a structure different from the ball valve in this invention.
Next, another U.S. Pat. No. 6,189,860B1 tilted “PLASTIC BUTTERFLY VALVE” includes a hollow cylindrical body 1 and a valve disk 4, which are separately fabricated and then combined together. This valve also has the same drawback of complicated manufacturing processes, expensive cost, and a structure different from the ball valve in this invention.